Polypropylene terephthalate and polybutylene terephthalate molding resins, along with polyethylene terephthalate were first disclosed in U.S. Pat. No. 2,465,319 to Whinfield and Dickson.
The utilization of polypropylene terephthalate and polybutylene terephthalate as molding resins is becoming increasingly accepted in recent years. For example, polypropylene terephthalate and polybutylene terephthalate can be molded and processed at lower temperatures, have a shorter cycle time in the mold and do not require, as does polyethylene terephthalate, the presence of either a nucleating agent or an internal mold release agent. Reinforced polypropylene terephthalate and polybutylene terephthalate molding resins surprisingly have been found to be superior to similarly reinforced polyethylene terephthalate in many important processing and performance characteristics. Furthermore, reinforced polypropylene terephthalate and polybutylene terephthalate molding resins have correspondingly higher tensile strength, lower water absorption and better creep (flexural) properties than does similarly reinforced polyethylene terephthalate.
Polypropylene terephthalate and polybutylene terephthalate, just as polyethylene terephthalate, however inherently possess the disadvantage of being flammable, and when burning tend to drip a significant quantity of flaming droplets. Such disadvantage limits their use to those applications where this shortcoming can be tolerated.
Various proposals have heretofore been made for reducing the burning characteristics of polypropylene terephthalate and polybutylene terephthalate. See, for instance, U.S. Pat. No. 3,751,396 to John S. Gall, and U.S. Pat. No. 3,624,024 to John R. Caldwell and Marvin A. McCall. It had been proposed, inter alia, to incorporate within the polypropylene terephthalate or polybutylene terephthalate an organic flame retardant additive such as decabromodiphenyl oxide, tetrabromophthalic anhydride, tetrabromobisphenol A diacetate, 3,4,5,6-tetrabromo-N-methylphthalimide, etc. Antimony trioxide may also be included. It has been observed, however, that the polypropylene terephthalate and polybutylene terephthalate molding compositions of the prior art which incorporate the various flame retardant additives heretofore proposed tend to possess properties which interfere with the appearance of molded articles formed from the same in some end use applications. For instance, the flame retardant additives heretofore proposed upon the passage of time tend to separate from the polymeric matrix and to exude from the same at elevated temperatures. The additive may become visually apparent upon the surface of the molded article as a fine powder.
Also, as discussed in U.S. Pat. No. 3,751,396 polypropylene terephthalate and polybutylene terephthalate molding compositions containing the flame retardant additives of the prior art may have a tendency drip flaming particles when subjected to flame. An approach to overcome this deficiency has required the additional incorporation of a supplemental reinforcing agent, such as asbestos, having a length to diameter ratio greater than 50:1.
In our commonly assigned U.S. Ser. Nos. 432,275 and 432,372, filed Jan. 10, 1974, are claimed superior polypropylene terephthalate or polybutylene terephthalate molding compositions which include certain brominated aromatic polyphosphates as the flame retardant additive.
It is an object of the present invention to provide a polypropylene terephthalate or polybutylene terephthalate molding compositions suitable for forming improved flame retardant three-dimensional shaped articles.
It is an object of the present invention to provide a flame retardant polypropylene terephthalate or polybutylene terephthalate molding composition which includes in intimate admixture therewith a flame retardant additive which is non-exuding from the resulting three-dimensional molded article even upon the passage of extended periods of time at elevated temperatures.
It is an object of the present invention to provide a flame retardant polypropylene terephthalate or polybutylene terephthalate molding composition which is capable of forming a molded three-dimensional shaped article which is non-dripping when subjected to flame even in the absence of asbestos.
It is an object of the present invention to provide an improved self-extinguishing polypropylene terephthalate or polybutylene terephthalate molding composition which is capable of forming a three-dimensional shaped article which passes the UL-94 Flammability Test.
These and other objects as well as the scope, nature, and utilization of claimed invention will be apparent from the following detailed description and appended claims.